Magnetic recording and reproducing apparatuses, typically, magnetic disk drives, have been required to provide higher data transfer rates and higher recording densities. This has resulted in the use of higher coercivity recording media. With regard to thin film magnetic heads, it is desired to maximize the coil current to recording magnetic field conversion efficiency since the recording frequency must be raised to cope with the demand for higher data transfer rate. To raise the conversion efficiency, the hysteresis loss of the magnetic cores should be reduced by using a low Hc/Hk material to lower their coercivity (Hc) along the hard axis or anisotropy magnetic field (Hk). Further, to reduce the eddy loss, the resistivity (ρ) of the material should be high.
Conventionally, low Hc(1.0-1.50 Oe) and high ρ(40-50 μΩcm) 52-58 wt % FeNi alloy plated films (Hk: 5-100 Oe, Bs: 1.65-1.75 T) have been used to constitute magnetic cores.
Further, as described in Japanese Laid-Open Patent No. 2005-63489 (“Patent Document 1”), a low Hc(0.5-1.5 Oe), low Hk(0.5-1.5 Oe) and high Bs (2.1-2.3 T) 84-92 wt % FeNi alloy plated film has been developed to realize higher frequency recording. Forming of a lustrous film having such properties is made possible by controlling the pH of the plating bath to an acidity value of 1.5-2.3. Otherwise, the film whitens or blackens due to the roughness of the plated surface if the Fe content is increased beyond 60 wt % (Fe≧60 wt %). Use of this 84-92 wt % FeNi in a thin film magnetic head improves its frequency response. Evaluation of thin film magnetic heads by using L=0.006 μH as a barometer level showed that 84-92 wt % FeNi raises the allowable frequency f to 700-800 MHz from the frequency of 500-600 MHz by 52-58 wt % FeNi. It was also found that this frequency can be raised further to 900-1000 MHz by thermal treatment. That is, use of the 84-92 wt % FeNi allows a thin film magnetic head to output the required level of magnetic field at higher recording frequencies.
In order to improve a magnetic disk drive in data transfer rate and recording density, the magnetic cores of the thin film magnetic heads should be made of a high performance magnetic film which does not exhibit either a large hysteresis/eddy loss or a large permeability (μ) decrease at high recording frequencies. As the properties of the material, low Hc, low Hk, high ρ and high Bs are required.
In order to solve this problem, a lustrous and uniform FeNi alloy plated film of which Fe content is 84-92 wt % was developed as described in Patent Document 1. Based on this material, the inventors successfully formed a low Hc (0.8 Oe), low Hk(1.0 Oe), high Bs(2.2 T) and high ρ (35 μΩcm) 88Fe12Ni plated film as the upper magnetic core and a similar 88Fe11Ni1Cr plated film (ρ: 40 μΩcm, Hc: 1.4 Oe, Hk: 2.0 Oe, Bs: 2.0 T) as the lower magnetic core. While the recording frequency can be raised up to 700-800 MHz, however, this composition cannot fully meet the demand for longitudinal/perpendicular recording thin film magnetic heads capable of recording at 1000-2000 MHz.